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Activity 4: Mountain Building

PUSHING AND PULLING MOUNTAINS

Summary:

Mountains and valleys are created by huge tectonic activity, or movement in the Earth. This movement occurs in many different ways, over millions of years. This lesson will show how mountains and valleys form as the result of tectonic forces.

Instructional Method: Activity

Goal: To experiment with how tectonic forces form mountains.

Objectives: Students will be able to:

Recreate each landform made by drawing it on paper or using the foam strips

Perform each force needed to create different landforms

Label on paper the direction of the movement of the rock corresponding to each force

Mountains and valleys form in many ways. Two types of tectonic forces can result in mountains and valleys: compression (squishing) and extension (pulling apart). These forces commonly associate with mountain building but also form valleys.

Compressing continents occur when two continents collide. In crustal collision, the buckling action of rock is similar to what happens to the hoods of cars in a head-on collision. The buckles form mountains and valleys. In rock the buckles can fracture and slide on top of each other, causing that area to increase in thickness.

An example of two continents compressing into each other resulted in the Himalayan Mountains. This happened when India collided with Asia millions of years ago. They are still compressing into each other and the mountains are still growing today.

An older example of the same thing happening in the United States is the Appalachian Mountains. North America and Africa collided about 200-300 million years ago forming this great mountain system. They are no longer growing but diminishing due to erosion over time. Great Smoky Mountains National Park is located in the heart of the Appalachians.

Stretching a continent causes it to thin and break in the same way silly putty breaks when it is cold and stretched quickly. Faults form throughout the stretched portion of the crust and allow large blocks of solid rock to move up or down as dictated by magma movement in the mantle. These massive blocks of rock are called fault blocks.

Fault blocks are divided into two categories: horsts and grabens. A horst is an uplifted fault block and a graben is a fallen or down dropped fault block. A geographic region in the western United States known for horst and graben fault block structures is the Basin and Range. This region begins at Zion National Park and extends into eastern California. A national park sharing the region's name and located within the Basin and Range is Great Basin National Park.

The Plateau region in the Four Corners area of the American southwest (southern Utah, northern Arizona, southeastern Colorado and northwest New Mexico) may have uplifted by the collision of two tectonic plates. However, this area did not get mangled and buckle like the Appalachian Mountains. Buckling occurred close to the plate contacts forming the Sierra Nevada mountains.

The Pacific Plate is thought to have slid under the American plate for a long distance until it sunk deep into the mantle. Once it was deep enough, it melted and the melted rock rose towards the surface. Rising magma uplifted the entire area forming the Colorado plateau. Much of the rising magma remained below the flat-lying crust.

Laccoliths and batholiths formed in locations on the Colorado Plateau where the magma did not break through the surface. These two landforms are like "blisters" of magma under the rocks. Eventually, the magma cooled and hardened forming a solid core of igneous rock. These igneous "blisters" exposed at the surface form batholiths and laccoliths . Batholiths are igneous intrusions with irregular shapes, top and bottom. Laccoliths are rounded on top and have a flat bottom. Scientists believed that because the igneous intrusion was pushed into flat lying horizontal layers the bubble's bottom spread along a bedding plane, giving it a flat bottom.

These blisters form the Henry mountains, Manti-La Sal mountains, San Francisco mountains and Navajo Mountain, among others. Each one of these mountain ranges can be seen from surrounding national parks; Arches National Park, Bryce Canyon National Park, Capitol Reef National Park, Canyonlands National Park and Hovenweep National Monument.

Many times a combination of extension and collision is responsible for the creation of landforms.

Instructional Procedures:

1. Instructional Procedures for Creating Activity Tools:

Cut foam into strips 2-4 inches wide and 8-12 inches long.

Cut two small holes into each end with scissors or a paper punch.

Alternate thickness and color to create a stack of 3 to 5 pieces.

Thread string through the holes cut in the foam to fasten the pieces together forming a foam sandwich.

Make sure the string is loose enough that the foam pieces can slide when bent.

Cut wood into angled pieces of 45 degrees or more.

Drill a hole through each piece so they line up.

Slide a rope through the blocks and tie a knot at each end. Make sure to leave 3 to 4 inches between the knot and the end of the block.

2. Activity Instructions:

The foam layers represent layers of rock. By pushing and folding the foam you can imagine how rock layers respond to the same forces. Obviously, folding and buckling mountains in nature takes a very long time, but the process is replicated quite well with foam.

Wood blocks represent portions of the crust as it responds to extensional forces. Start with the blocks pushed together forming a flat surface and then pull them apart to form mountains and valleys. In nature, the higher portions are called horsts and the falling portions are called grabens.

Explain what the layers of foam represent and what the wood blocks represent. If possible show pictures of landforms that show the rock layers with folds or bends. A topographic or geologic map of Nevada would be helpful to show the mountains and valleys formed by stretching the crust.

Demonstrate to the class the different types of mountain building processes.

Give a demonstration on how they can use each tool to build their own mountains.

Break students into as many groups as possible so that each group can have their own foam and blocks.

Recreate each landform they have studied.

Draw on a paper the forces, noted by arrows, that are responsible for creating each landform.

Discussion:

What are the different forces that build mountains? How do they work? Are there any mountains near you? If so, do you know how they formed? Can we ever feel mountains moving (yes, earthquakes)? What do we call the shaking we feel when there is movement along a fault?

Variation:

If foam is not available, try using short stacks of different color paper. Each stack of paper should represent one rock layer. Stacks should be at least 1/8 inch thick and no more than 1/2 inch thick. Each stack should be a different color. Follow steps 2-5 of procedures for building tools in order to create paper rock layers, then proceed with activity.

Extension:

Have students hypothesize what may happen if forces were placed in different locations or from only one side, etc. Write down the hypotheses. Perform the hypotheses on the foam layers and blocks. Write down what happened to the foam and blocks ( i.e. what landforms they created).